Plate Tectonics

Dr. Ahmad Redaa

2024-10-28

Alfred Wegener: The Father of Plate Tectonics

  • Who was Alfred Wegener?
    German meteorologist and geophysicist who proposed the Continental Drift Theory in 1912.

  • Continental Drift Theory
    Wegener suggested that continents were once part of a supercontinent called Pangaea and have since drifted apart.

  • Evidence Supporting Continental Drift

    • Fossil Distribution: Similar fossil species found on continents now separated by oceans.
    • Rock Formations: Similar rock types and mountain ranges on now-separated continents.
    • Paleoclimate Indicators: Unusual climate evidence, like glacial deposits in tropical regions.
  • Initial Reception:
    Skepticism due to lack of a plausible mechanism for continental movement.

Alfred Wegener a few years before his death in 1930. Source: Steven, E. (2015)

Global Geological Models of the Early 20th Century

Prevailing Theories Before Plate Tectonics

  1. Contractionism
    • Theory: Earth is slowly cooling and shrinking, causing the formation of mountain ranges like “wrinkles on a dried-up apple.”
    • Problems:
      • Insufficient cooling to cause necessary shrinking.
      • Conflicts with the Principle of Isostasy (prevents continents from sinking).
  2. Permanentism and Geosyncline Theory
    • Permanentism: Belief that continents and oceans have remained generally the same.
    • Geosyncline Theory: Suggested that mountain chains formed from thick deposits of sediments along continental margins.
    • Geosynclines: Depressions filled with sediment, explaining sedimentary layering but lacking support for large-scale continental movement.

Continental Drift Theory

The distribution of several Permian terrestrial fossils that are present in various parts of continents that are now separated by oceans. Source: Steven, E. (2015)

Seafloor Spreading

Pattern of sea-floor magnetism off of the west coast of British Columbia and Washington. Source: Steven, E. (2015)

Plate Tectonics Theory

The layers of the tectonic Earth, (Source: Jain, S. (2014))

Types of Plate Boundaries

The Ocean–Ocean convergence

The Ocean–Ocean convergence, (Source: Jain, S. (2014))

The Ocean–Continent convergence

The Ocean–Continent convergence, (Source: Jain, S. (2014))

The Continent–Continent Collision

The Continent–Continent Collision, (Source: Jain, S. (2014))

Divergent Plate Boundary

The Divergent Plate Boundary, (Source: Jain, S. (2014))

Example of Divergent Plate Boundary

The East Africa Rift Valley and the Red Sea rift, (Source: Jain, S. (2014))

Hot Spots and Mantle Plumes

Schematic model for oceanic volcanism

Schematic model for oceanic volcanism, Source: Winter, J. (2014)

Plate Tectonics and Volcanism

Plate Tectonics and Metamorphism

Summary